1. Field of the Invention
The present invention is related to the protection of electronic systems and, in particular, to a high-speed short circuit protection module.
2. Background Information
Reliable high-speed short circuit detection presents a challenge to the circuit designer for a number of reasons. For example, the short-circuit protection device must be able to correctly distinguish among a voltage drop caused by a short circuit, a voltage drop resulting from a load power requirement, a voltage drop caused by switching noise, and a voltage drop caused by removal and replacement of the power supply. That is, a fault signal should be generated only in response to the occurrence of a short circuit condition. It is undesirable for an electronic system to be inadvertently powered down because of noise, variable power demand, or routine maintenance of the system.
Additionally, if the short-circuit protection device is used with a low impedance power system, such as commonly found in high-current computer systems, the power system exhibits a very low voltage drop at high current loads. Moreover, in certain applications, the voltage to be monitored is the same voltage used to power the short circuit detection circuitry. It then becomes a requirement that the detection circuitry self-bias as no other xe2x80x98start-upxe2x80x99 voltage is available.
What is needed is an improved, high-speed, short circuit protection module, and it is an object of the present invention to provide such a device.
It is a further object of the present invention to provide a method of distinguishing a short-circuit condition from the occurrence of high-frequency noise.
It is another object of the present invention to provide a short-circuit protection module which allows for the replacement of a power supply without causing a power-down of the electronic system.
It is yet another object of the present invention to provide a short circuit protection module which can be used to monitor its own supply voltage. Other objects of the invention will be obvious, in part, and, in part, will become apparent when reading the detailed description to follow.
The disclosed short circuit protection device exhibits a very short response time, is not triggered by high-frequency noise, and provides for normal power down or removal of a monitored power supply without shutting down the entire electronic system. In a first embodiment the protection device includes a comparator with a non-inverting input port, an inverting input port, and an output port, and is used with first and second voltage reference signals obtained from the power supply to indicate a short-circuit condition when the reference signals are the same. A first voltage divider is connected to the power plane of the monitored power supply and provides the first reference signal to the non-inverting input port, and a second voltage divider is connected to the power supply output and provides the second reference signal to the inverting input port, where the second reference signal is normally smaller than the first reference signal.
A first time constant between the first voltage divider and the non-inverting input port provides a first time delay to the first reference signal, and a second time constant between the second voltage divider and the inverting input port provides a second time delay to the second reference signal, where the second time delay is greater than the first time delay. When a short-circuit condition occurs, the voltage levels of the reference signals become the same, changing the status signal at the comparator output port, and signaling a power-down of the power supply. In a second embodiment, a diode and the first voltage divider are connected to the power supply output and the second voltage divider is connected to the diode.
A short circuit protection system includes a short circuit protection device in accordance with the first embodiment and at least one short circuit protection device in accordance with the second embodiment, where the output of the first embodiment protection device and the output of the one or more second embodiment protection device(s) are connected to a fault signal subcircuit. The output of the fault signal subcircuit provides a status of the two or more monitored power supplies, where the fault signal circuit output assumes a first logic state when the voltage levels of all first reference signals remains greater than the corresponding second reference signals. On the other hand, the fault signal circuit output assumes a second logic state, indicating the presence of a short circuit condition in one of the power supplies, when at least one first reference signal is the same as the corresponding second reference signal.